Mizusawa Kanta, Kasagi Satoshi, Takahashi Akiyoshi
School of Marine Biosciences, Kitasato University, 1-15-1 Kitasato, Minami-ku, Sagamihara, Kanagawa 252-0373, Japan.
School of Marine Biosciences, Kitasato University, 1-15-1 Kitasato, Minami-ku, Sagamihara, Kanagawa 252-0373, Japan.
Gen Comp Endocrinol. 2018 Dec 1;269:141-148. doi: 10.1016/j.ygcen.2018.09.006. Epub 2018 Sep 5.
Melanosome dispersion is important for protecting the internal organs of fish against ultraviolet light, especially in transparent larvae with underdeveloped skin. Melanosome dispersion leads to dark skin color in dim light. Melanosome aggregation, on the other hand, leads to pale skin color in bright light. Both of these mechanisms are therefore useful for camouflage. In this study, we investigated a hormone thought to be responsible for the light wavelength-dependent response of melanophores in zebrafish larvae. We irradiated larvae using light-emitting diode (LED) lights with peak wavelengths (λ) of 355, 400, 476, 530, and 590 nm or fluorescent light (FL) 1-4 days post fertilization (dpf). Melanosomes in skin melanophores were more dispersed under short wavelength light (λ ≤ 400 nm) than under FL. Conversely, melanosomes were more aggregated under mid-long wavelength light (λ ≥ 476 nm) than under FL. In addition, long-term (1-12 dpf) irradiation of 400 nm light increased melanophores in the skin, whereas that of 530 nm light decreased them. In teleosts, melanin-concentrating hormone (MCH) aggregates melanosomes within chromatophores, whereas melanocyte-stimulating hormone, derived from proopiomelanocortin (POMC), disperses melanosomes. The expression of a gene for MCH was down-regulated by short wavelength light but up-regulated by mid-long wavelength light, whereas a gene for POMC was up-regulated under short wavelength light. Melanosomes in larvae (4 dpf) exposed to a black background aggregated when immersing the larvae in MCH solution. Yohimbine, an α-adrenergic receptor antagonist, attenuated adrenaline-dependent aggregation in larvae exposed to a black background but did not induce melanosome dispersion in larvae exposed to a white background. These results suggest that MCH plays a key role in the light wavelength-dependent response of melanophores, flexibly mediating the transmission of light wavelength information between photoreceptors and melanophores.
黑素体分散对于保护鱼类内部器官免受紫外线照射很重要，尤其是在皮肤发育不全的透明幼体中。黑素体分散会导致弱光下皮肤颜色变深。另一方面，黑素体聚集会导致强光下皮肤颜色变浅。因此，这两种机制都有助于伪装。在本研究中，我们研究了一种被认为负责斑马鱼幼体黑素细胞对光波长依赖性反应的激素。我们在受精后1 - 4天（dpf）使用峰值波长（λ）为355、400、476、530和590 nm的发光二极管（LED）灯或荧光灯（FL）照射幼体。皮肤黑素细胞中的黑素体在短波长光（λ≤400 nm）下比在FL下更分散。相反，黑素体在中长波长光（λ≥476 nm）下比在FL下更聚集。此外，400 nm光的长期（1 - 12 dpf）照射会增加皮肤中的黑素细胞，而530 nm光的照射则会减少它们。在硬骨鱼中，黑色素浓缩激素（MCH）使色素细胞内的黑素体聚集，而源自阿黑皮素原（POMC）的促黑素细胞激素则使黑素体分散。MCH基因的表达在短波长光下被下调，但在中长波长光下被上调，而POMC基因在短波长光下被上调。将暴露于黑色背景的幼体（4 dpf）浸入MCH溶液中时，幼体中的黑素体聚集。育亨宾，一种α - 肾上腺素能受体拮抗剂，减弱了暴露于黑色背景的幼体中肾上腺素依赖性聚集，但在暴露于白色背景的幼体中未诱导黑素体分散。这些结果表明，MCH在黑素细胞对光波长的依赖性反应中起关键作用，灵活地介导光感受器和黑素细胞之间光波长信息的传递。
